The conventional etching methods are described in, for example, Patent Document 1 or Patent Document 2. Patent Document 1 describes an etching method in which a pulse plasma process is performed on a first layer of a sample and a continuous plasma process is performed on a second layer to remove a part of these layers. Since the layers in Patent Document 1 have different compositions, the different plasma processes are performed. Patent Document 2 describes an etching method in which a continuous plasma process is intermittently carried out.    Patent Document 1: Specification of U.S. Pat. No. 7,737,042    Patent Document 2: Specification of U.S. Pat. No. 7,718,538
However, if there are different compositions, the densities thereof are also different. Therefore, when these layers are etched at the same time, there is a difference in etching rates. Recently, along with the development of a manufacturing technology for electronic elements such as a fin-type transistor, there has been an increasing demand for a technology of etching regions having different densities at the same etching rates.